Visually very similar to H2, with subtle improvements. I like that very much. Didn't try to go overboard on moving plants or water that no one cares about after seeing it once.
New weapons. Spike grenade: weak at distance, disgustingly deadly at zero range. A good meaty "thwack" means the thrower needs to go hide for a few seconds. It's supper time.
Spartan laser: hard to use, but presumably gets easier with practice.
Assault rifle: nice. Default spawning weapon. Shoots well in bursts.
Gotta go. Master Chief needs taught a Covenant lesson tonight.